Full text of "The treatment of lime-induced chlorosis with iron salts"

See other formats

UNIVERSITY OF CALIFORNIA

COLLEGE OF AGRICULTURE

AGRICULTURAL EXPERIMENT STATION

BERKELEY, CALIFORNIA

CIRCULAR 321
March, 1931

THE TREATMENT OF LIME-INDUCED
CHLOROSIS WITH IRON SALTS

J. P. BENNETTi

The leaves of some plants when growing- in soils containing an
excess of lime become more or less yellow. This yellow condition is
known generally as chlorosis, and when caused by an excess of lime in
the soil, as lime-induced chlorosis. Lime in excess interferes with the
absorption and utilization of iron by the plant. The failure to receive
a normal iron supply results in leaves not forming the full amount
of the green leaf pigment known as chlorophyll.

Lime-induced chlorosis usually appears first on the younger por-
tions of the more rapidly growing shoots, and in perennials it spreads,
during the following years, to older parts of the plant, In annual
plants it is usually most severe on younger portions of the plant and
may involve only a small part or nearly all of the plant. Light
attacks usually do not cause much injury; but in severe attacks the
plant may be severely stunted, fail to blossom or fruit, drop its leaves
early, and it usually dies prematurely.

Soils containing an excess of lime usually contain also an abun-
dance of iron but in a form insufficiently available to many plants.
It has proven generally impracticable, thus far, to make the iron in the
soil available, or to increase the amount of available iron present by
the surface addition of fertilizers containing iron. The presence of
excess lime in the soil quickly renders applied iron insoluble and
unavailable. The only practicable, immediate cure for lime-induced
chlorosis is to apply iron in suitable form and amount directly to the
plant.

i Associate Professor of Plant Physiology and Associate Plant Physiologist
in the Experiment Station.

2 University of California — Experiment Station

It has long been known that lime-induced chlorosis can be remedied
by direct application of iron to the plant. E. Gris,2 in 1843 in France,
first found that iron sulfate applied to chlorotic plants through roots
or leaves caused them to become green. Since that time treatment
of chlorosis has been more or less common in Europe. The applica-
tions have been made by spraying the leaves or by introducing the
iron in suitable form directly into the roots, trunk, or branches of
the plant.

The occurrence of yellow leaves during the growing season may
be due to several other causes than an excess of lime. And it is not
possible by an examination of the affected leaves to recognize the
cause of yellowing. If the cause is an excess of lime this may usually
be easily determined by an examination of the soil in which the tree
roots are growing.

EXAMINING THE SOIL FOR LIME

A simple and often sufficient determination of the presence of lime
may be made by pouring some muriatic acid on to the soil. If it foams
strongly it probably contains lime in sufficient amount to cause
chlorosis. The lime may not be present in the surface soil so it is
necessary to examine it at various depths. This may be done most
easily by boring with a soil auger or tube, keeping the soil from
different depths separate and applying acid to each sample. The
lime is often found near the surface but in some cases it may be neces-
sary to sample to a depth of six feet or more. If no evidence of lime
is obtained by such an examination the yellowing is probably due to
some other cause. For a more accurate determination samples of the
soil may be taken to a chemist. Any lime content of one per cent or
over is likely to cause chlorosis of certain trees, especially pear, and a
content of one-half to one per cent may be viewed with suspicion.

The more common, commercially-cultivated trees which show lime-
induced chlorosis are pear, apple, quince, peach, apricot, prune, plum,
cherry, walnut, orange, and lemon. Raspberries also suffer severely.
Among ornamental plants eucalyptus, acacia and many other trees
and shrubs are known to show chlorosis in high-lime soils. Pear trees
grafted on Japanese or quince rootstocks develop chlorosis on high-
lime soils much more quickly and severely than do those on French
stocks. Stone fruits on myrobalan stocks generally show little or no
chlorosis, while peaches and apricots on peach stocks may suffer
severely. Observations on the effects of other stocks are not available.

2 Gris, E. N/ouvelles experiences sur 1 'action des composes f errugineux soluble,
appliques a la vegetation, et specialement au traitment de la chlorose et de la
debilite des plantes. C. R. Acad. Sci. (Paris) 17:679. 1843.

Cir. 321] Treating Lime-Induced Chlorosis with Iron Salts 3

TREATING THE TREE

There are four successfully used methods of treating' plants with
iron salts for lime-induced chlorosis: spraying, trench applications,
solution-injection, and dry-salt treatment.

Spraying. — Spraying iron solution on the leaves has not proved to
be commercially successful with fruit trees, on account of difficulties
in securing good distribution on the leaves and because repeated spray-
ings are necessary during the growing season as new leaves develop.
With few plants to be treated, spraying may easily be used. A solu-
tion of ferrous sulfate (copperas) one ounce per gallon of water, with
the addition of one teaspoonful of liquid glue as a spreader, and a
suitable sprayer, is all that is required. The spraying should pre-
ferably be done very late in the day so that the solution will not dry
on the leaves and the iron may be absorbed during the night. The
leaves should be thoroughly covered by the spray. The concentration
of the iron solution mentioned has been found satisfactory for fruit
trees with full-grown leaves; it may have to be reduced for tender
foliage. The spraying should not be done while the plant is in bloom
because of probable injury to flower parts. Limited trial applica-
tions should be made on plants where no previous experience is avail-
able, followed by observations for a few days before general treatment
is applied. The treatment lasts but one season.

The Trench Method. — In this method of treatment, introduced
widely in Europe in 1886 by Sachs,3 a well-known German botanist,
trenches several inches wide are dug around the tree to a depth of
one to two feet, and one to several feet from the base of the tree so
as to expose many small roots. Ferrous sulfate (copperas), crushed
so that the largest lumps are about one-half inch through, is strewn
along the trench bottom. The amount to be used increases with the
size of the tree. The dimensions of trenches and the amounts of iron
salt to use for trees of different sizes are suggested in the first four
columns of table 1. Modifications of the amounts of iron salt indi-
cated may have to be made as a result of experience. After spreading
the iron salt in the bottom the trench is refilled with soil and heavily
watered.

The same treatment may be applied by boring holes in the soil
with a soil auger, about two inches in diameter. These should be one
to two feet deep and two to three feet apart, in one or more rings
around the tree spaced from one to several feet distant from the

3 Sachs, J. Das Eisen und die Chlorose der Pflanzen. Naturw. Rundschau
1:257-259. 1886.

4 University of California — Experiment Station

trunk. The numbers and depths of holes and amount of iron salt per
hole is indicated in the last three columns of table 1. The total dose
per tree is the same as when applied in trenches. After putting the
iron sulfate in holes water freely and fill with soil. This modification
of the trench method was originated by Hendrickson in 1924.4

TABLE 1

Trenches, Holes, and Dosage for Treating Non-Bearing*

Trench Method

Trees by the

Diameter

Trenches, 8-12 inches wide

Amount of

ferrous sulfate

per tree,

pounds

Auger holes, 2-inch diameter

Amount of

ferrous sulfate

per hole,

of tree,
inches

Distance from
tree, feet

Depth,
inches

Number

Depth,
inches

n *

0 25

0 5

\Vi

0 7

tyl

0.7

1.0

v-A

iVi

1.0

*For bearing trees the dosage should be reduced to about one-half or two-thirds of that indicated
the table unless experience has shown there is no danger of injury to the blossoms.

The object in both the above applications is to bring the iron salt
in contact with or very near to the smaller roots so that it may be
absorbed before it becomes insoluble in the alkaline soil. The dosage
indicated above is not intended to be fixed but is suggested as a trial
dose. If it proves to be too large some burning and blackening of
foliage will occur in the early spring, but usually it is not severe and
does not affect the later leaves. Burning may be avoided by decreas-
ing the amount applied. On the other hand, the dosage given may be
too small or not well distributed and an incomplete cure may result.
It is essential that the amount applied be sufficiently large and that
it be well distributed on all sides of the tree, to get satisfactory results.
The dosage suggested may serve as a general guide until experience
is gained with the soil and trees at hand. Other iron salts than fer-
rous sulfate have not been extensively used in trench applications on
account of expense.

4 Hendrickson,
Sci. 1924:87-90.

A. H. A chlorotic condition of pears. Proc. Amer. Hort.

Cir. 321] Treating Lime-Induced Chlorosis with Iron Salts 5

The application is preferably made in the late winter or spring
just before leaves appear. It may be done after the leaves unfold
but there is then much greater likelihood of burning the foliage and
the dosage should be decreased to one-half, or less, of that indicated
above. It will readily be seen that the treatment described above is
expensive in labor, and also in iron salt since large amounts of it are
required and most of that used does not reach the tree but is lost in
the soil. It has been successfully used, especially on ornamental
plants. It may be used where but few plants are to be treated and
expense is not a serious consideration, and where there is objection to
the wounding of trees involved in the methods to be described next.
Some use has been made of the trench application in commercial
orchards by plowing deep furrows near the tree rows and spreading
iron sulfate in the furrows at the rate of 500 to 2,000 pounds per acre
in the early spring before leaves appear. This has sometimes resulted
in cures and sometimes in complete failure. When applied carefully
in trenches, or in auger holes, with watering afterward, the results
are generally good. Successful applications of iron sulfate to chlorotic
raspberry plants have been made by using one to two pounds per ten
feet of row in trenches or furrows several inches deep close to the
base of the plants.

The Injection of Solutions of Iron. — In this method, also origi-
nated by Sachs, iron is introduced into the tree in solution in water.
In the usual procedure any soluble iron salt such as iron sulfate (cop-
peras), iron chloride, iron nitrate, ferrous or ferric citrate or tar-
trate, or iron ammonium citrate, is dissolved in water at the rate of
one ounce per gallon. In trees up to six inches in diameter a single
hole, one-fourth to three-eighths inch in diameter is bored about two-
thirds to three-fourths through the trunk, with the bottom of the hole
somewhat lower than the mouth. Into the hole is screwed tightly a
short length of threaded pipe and above this a suitable " reservoir is
attached, directly, or by a rubber tube. Iron solution is placed in
this reservoir in an amount determined by the size of the tree. Air
must be displaced from the hole and connections in order to prevent
blocking of flow and absorption of solution. This is readily accom-
plished by filling the hole and pipe with solution before attaching
the reservoir. For larger trees, in order to secure good distribution of
the iron solution, two or more such reservoirs are attached separately,
to holes bored parallel to each other from one side of the tree and
three to four inches apart ; or to holes bored toward the center of the
tree to a depth of four to six inches and at intervals of six to eight

6 University of California — Experiment Station

inches around the tree. The latter arrangement of holes is preferable
for trees with well-developed heartwood. The holes may also be bored
in the larger roots or in the base of the trunk below the ground level,
or in branches. The number and depth of holes per tree and the
amount of solution for trees of different sizes are indicated in table 2.
This table is intended only as a guide and may require modification
according to experience. The solution of iron is gradually absorbed
by the wood and passes mostly toward the branches. The rate of
absorption may be hastened by raising the reservoir. Trees that exude
sap or bleed from wounds cannot be injected during the season of
bleeding. After treatment the holes are covered with grafting wax.

TABLE 2

Dosage and Holes for Treating Non-bearing* Chlorotic Trees by the
Solution-Injection Method

Tree diameter,

Holes, 5^-inch diameter

Amount of

inches

Number

Depth, inches

solutionf, pints
per tree

iy2

10-12

10-17

* For bearing trees the dosage should be reduced to about one-
half or two-thirds of that indicated in the table unless experience has
shown there is no danger of injury to the blossoms.

t Based on a solution of one ounce per gallon.

This treatment gives best results if applied during the dormant
season when leaves are absent. If applied during the leafy season
the iron solution passes rapidly to the leaves and may cause severe
burning and loss of part or all the leaves and of the blossoms or fruit.
The treating of evergreens by this method should be done preferably
in winter when absorption will be slower.

In all treatments by injection of iron solutions when leaves are
present the strength of the solution should be reduced to about one-
fourth that used in treating leafless trees and the total dose per tree
should be correspondingly reduced to avoid injury to the leaves.
Successful results with this method of treatment are dependent upon

Cm. 321] Treating Lime-Induced Chlorosis with Iron Salts 7

applying- a sufficiently large dose and in securing good distribution
of the iron salt by applying through a sufficient number of holes.

Dry-Salt Treatment. — It was found by Mokrzecki5 to be unneces-
sary to dissolve the iron salts in water before introducing them into
the tree. Wood contains about fifty per cent water and if a soluble
iron salt is placed in a hole bored in live wood and the mouth of the
hole sealed the salt absorbs water from the wood and dissolves and
passes into the surrounding wood from which it passes to the branches
with the sap stream. In applying this treatment % to %6-inch holes
are bored in the larger roots, in the trunk above or below the ground
level, or in branches. The holes should be bored at intervals of three
to four inches around the root, trunk, or branch and from one to three
inches deep. In the bottom of each hole is placed from y1Q0 to %
ounce of ground iron salt. The hole and the amount of salt used
should be so proportioned that the mass of salt does not come closer
than half an inch from the mouth of the hole, in order to avoid burn-
ing of the bark around the hole by the salt. The mouth of the hole is
then covered with a suitable wax. The number and depth of holes
and dosage for trees of different sizes is shown in table 3.

TABLE 3
Dosage and Holes for Treating Non-bearing* Chlorotic Trees by the

Dry-salt Method

Holes

Amount of salt

Tree diameter,

inches

Number

Diameter,

Depth,

Per hole,

Per tree,

inches

ounces

0.01

0 01

0 02

0 05

7/fe

0 03 +

0 05

0.2

0 06

0 3

Mxs

0 08+

0.6

0 09

0 7

7/f6

0 09

0 8

7/fs

IVi

0.1

1.0

7/f6

0.1

7^6

0 1

2.0

* For bearing trees the dosage should be reduced to about one-half or two-thirds of that indicated in
the table unless experience has shown there is no danger of injury to the blossoms.

Table 3 was developed from experience in treating pear trees. It
may or may not apply to other trees of similar size. The dosage

s Mokrzecki, S. A cure for chlorosis. Gard. Chron. 35:36. 1904.

8 University of California — Experiment Station

should be proportional to the weight of the tree. The reference of
dosage to diameter is convenient but will apply only to trees of similar
height. For trees which are much taller than pear trees for a given
diameter, such as eucalyptus, the dosage shown above may be safely
doubled. In general the table should be considered only as a general
guide, so far as dosage is concerned. It is adapted to pears, but other
trees may require larger or smaller doses.

The tools for applying the treatment are few : an ordinary brace or
breast drill ; ordinary wood bits, 14-inch for trees less than two inches
in diameter, %f)-inch for all larger sizes; a bit extension two to three
feet long; a %-inch thin- walled metal tube about eight or nine inches
long, with a close-fitting metal plunger about three inches longer than
the tube, for placing the powdered salt in the holes; a similar tube
of ^-inch diameter with plunger for small trees ; and a pot of wax.
A %-inch tube with walls y32 inch thick holds about %0 ounce of
ground iron salt per inch of length when moderately packed ; a
%-inch tube holds about ^00 ounce per half inch of length. If a
large number of trees are to be treated a powder 'gun' may be con-
structed according to the diagram (fig. 1H). This instrument saves
much time in placing the powdered salt in the holes. Boring the
holes somewhat downward instead of horizontally also facilitates the
placing of the powdered salt and prevents it from spilling back on to
the bark.

If the applications are to be made below ground level soil is
removed from around the base of the trunk to a depth of three or
four inches. After covering the holes with wax the soil is replaced
immediately if soft grafting wax is used ; or several hours later if
emulsified asphalt is used, to allow the emulsion to dry somewhat and
stick to the bark. In all applications the powdered iron salt is pre-
ferably placed in the holes and these sealed within a, few hours after
boring; the holes should not be allowed to dry out inside.

Any sufficiently soluble iron salt will bring about a cure of chlo-
rosis when applied in the above manner. Among many salts tried
experimentally, ferrous and ferric citrate have given the best results.
The latter salt is manufactured only for the drug trade and retails
for about $1.25 to $1.75 per pound. It may be obtained through any
drug or chemical supply house. Ferrous citrate is manufactured in
a technical grade especially for treating chlorotic trees. It may be
obtained from chemical supply houses for about 75 cents per pound
under present market conditions. Both salts should be purchased
ground to pass a 60-mesh-to-the-inch screen, and will keep indefinitely

Cir. 321] Treating Lime-Induced Chlorosis with Iron Salts

^^,<W-

// W \\\\ £

Fig. 1. — A, Injection apparatus attached to tree; B, threaded, tapered, and
bored screw for injection of solutions; C, D, showing- manner of boring holes for
injection of solutions; E, F, showing manner of boring holes for dry-salt treat-
ment; G, plain tube with plunger for placing ground iron salts in holes; R, 'Gun'
for placing ground iron salt in holes.

10 University of California — Experiment Station

if kept dry. Other iron salts such as iron chloride, iron sulfate (cop-
peras), iron nitrate, iron tartrate, and iron ammonium citrate may
be used for treating* trees. Some of them, however, are less con-
venient to handle on account of becoming" sticky through absorbing
moisture from the air, and none of them have, in experimental tests,
given as uniformly good results as ferrous or ferric citrate.

Soft grafting wax suitable for underground use is made by melting
4 pounds rosin, 2 pounds beeswax, and mixing with an equal volume
of linseed oil ; or it can be made by melting hard grafting wax and
mixing with about one-half its volume of linseed oil. The wax handles
easily with a paddle. For use above ground an ordinary grafting
wax softened by heating may be used. The wax should not be so soft
that it runs into the hole. Emulsified asphalt preparations serve well
if suitably modified, but do not stick to the tree so well in wet weather
and often contract away from the side of the hole when exposed for
long periods. For use they are mixed with sufficient flour or starch
to give the desired consistency for handling with a paddle and to
prevent running into the holes ; and a little crude creosote or carbolic
acid is added to prevent the growth of molds.

In treating by injection of solutions or by the dry-salt method it
will be necessary to sterilize instruments before each operation to
guard against spreading infectious diseases such as pear blight, citrus
gummosis, etc. The usual solution for this purpose is one part of cor-
rosive sublimate and one part of mercuric cyanide to 500 parts of
water.

RESULTS OF TREATMENT

If maximum doses are used, the trench, injection and dry-salt treat-
ments will last about three years on pears. The first year, after treat-
ment, the leaves should be fully green over all the tree. An occasional
twig or larger branch may be yellow. During the second and third
year chlorosis gradually shows again, coming on first at the tips of the
more rapidly growing shoots, and may involve most of the length of
the shoots the third year. Spur leaves usually remain green through-
out the period so that fruiting is not affected directly. Shoot growth
is strongly stimulated by treatment of trees that have not become
severely stunted.

The best results by the trench, solution-injection, and dry-salt
methods are obtained when the treatment is applied during the dor-
mant season when leaves are absent. Treatments may be made during
the leafy season but no effect except greening of the leaves is pro-
duced the first season when application is made later than June.

Cm. 321] Treating Lime-Induced Chlorosis with Iron Salts 11

In re-treating, the previously bored holes should be avoided. Some
wood is killed near the hole and above and below it. Absorption of
solution or of dry-salt applications does not occur well through dead
wood. The holes are overgrown with new wood and bark usually the
first year after treatment so that their location can be ascertained at
re-treatment time only by boring; after locating one the others can
easily be avoided. The amount of wood removed by boring and killed
by the chemical is not large, amounting to about 20 per cent of the
cross section at the level of boring, and is about offset by a single
year's growth. No case of breakage resulting from boring has thus
far occurred in several years of treatments including several renewal
treatments.

When leaves appear the first time after treatment with the proper
dose there is usually some burning and blackening of the first small
leaves that come from the bud. These fall in a short time and suc-
ceeding leaves are green and uninjured. When overdosage has
occurred the burning of leaves may extend to later -appearing spur
leaves and even to shoot leaves. Killing of branches is unusual with
overdosage because the leaves which are killed carry away much of
the excess salt,

There is some difference among pear varieties in likelihood of
injury by overdosage. Bartlett and Hardy appear to be least liable to
be injured ; Winter Nelis most liable. The other varieties so far as is
known appear to be slightly more sensitive than Bartlett and Hardy.
The dosage suggested in table 2 applies to all varieties tested except
Winter Nelis in which one-half to two-thirds of the indicated dose
should be used.

In treating bearing trees some cases of blossom burning have
occurred, especially with Winter Nelis. For bearing trees the dosage
should be reduced to one-half or two-thirds that given in the tables
unless experience has shown that there is no danger. When correct
treatment is applied the effects on the crop of chlorotic trees which
are still bearing is evident the first year in a heavier set of fruit
amounting to as much as 100 per cent increase over untreated trees.
The full effects of treatment on bearing are not shown until the second
year when fruit buds formed during the first year of treatment may
result in increases of fruit of several hundred per cent, over untreated
trees. Severely injured, stunted trees, which have ceased bearing
before treatment, become green as a result of treatment but may not
resume bearing or growth for some time. It is doubtful whether or
not it is economical to retain and treat such trees.

12 University op California — Experiment Station

On trees other than pears no extended experience is available.
The last three methods of treatment as described have been used
successfully on peaches, plums, prunes, cherries, walnuts, eucalyptus
and many other ornamental shrubs and trees. With slender-stemmed,
woody plants, such as very young* trees, raspberry bushes, and herba-
ceous forms, only the trench method can be economically and safely
used. The cost of treatment varies principally with the size of the
trees; larger trees require more iron salt and more labor for applica-
tion. No figures are available as to cost of the trench and solution-
injection treatments. Treatments on a commercial scale with good
tools by the dry-salt method have been found to cost about one cent
per hole for iron salt, wax, and labor, so that trees five inches in
diameter would cost five cents and trees ten inches in diameter ten
cents per tree. A total of about 75,000 pear trees have been success-
fully treated by the dry-salt method, mostly by the growers them-
selves.

None of the described methods are to be looked upon at the present
time as permanent practices for the prevention of lime-induced chlo-
rosis. They are rather to be considered as temporary remedies to be
used to recover on an already heavy investment. A more satisfactory
and possibly permanent remedy should be sought through the soil.
A promising method of attack along" this line has recently been
described by Wallace6 in England. It consists simply of "grassing
down" the orchard with alfalfa, clover, or grass and fertilizing if
necessary with nitrogen, applied preferably as ammonium sulfate to
meet the extra demand of a double crop. A satisfactory cure required
three years. This method is under trial by a few growers in Califor-
nia. Whether or not it can be satisfactorily used under dry summer
conditions remains to be demonstrated ; but the possibility demands
consideration as offering a permanent solution to the problem of lime-
induced chlorosis.

6 Wallace, T. Investigations on chlorosis of fruit trees. IV. The control of
lime-induced chlorosis in the field. Jour. Pom. and Hort. Sci. 7:251-269. 1929.

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "The treatment of lime-induced chlorosis with iron salts"

See other formats